The present invention relates generally to grading, or landleveling, a tract of land to a desired finish contour and, more particularly, to an earthmoving apparatus and method for grading a parcel of land wherein a contour map is displayed to the operator of the earthmoving apparatus and is continually updated during the grading process. The contour map incorporates topographical changes in the land as the earthmoving apparatus traverses the tract until the desired finish contour is obtained.
Landleveling is a process commonly used in the agricultural industry to control water flow and accumulation on a field. Typically, the field is initially topographically surveyed and a graphical representation of its existing contour is produced. Based on this graphical representation of the existing land contour and a predetermined desired finish contour of the land, a contour map having cut and fill lines is created. Although cut and fill lines resemble conventional contour lines, which denote constant or iso-elevation, such cut and fill lines actually indicate the amount of cut or fill necessary to reach the desired finish contour. The operator of the earthmoving apparatus then uses the contour map as a guide in landleveling the field.
Operators of earthmoving equipment have experienced a significant problem with the contour map of the above described system. During the landleveling process, the cut and fill lines on the contour map remain unchanged even though the contour of the land has changed. Thus, the map becomes less useful as the work proceeds. Frequently, the field has to be re-surveyed before reaching the desired finish contour.
U.S. Pat. No. 4,820,041 issued to Davidson et al discloses a laser-based position sensing system for grading a tract of land with an earthmoving apparatus. The tract of land is surveyed and a site plan is drawn up illustrating the desired finish contour. From the tract survey and the site plan, a cut-fill map is produced showing amounts of cut or fill needed in individual portions of the tract of land to produce the desired finish contour. The information in the cut-fill map is then stored in a computer on the earthmoving apparatus.
The earthmoving apparatus is equipped with a laser receiver mast which is coupled to the grading implement of the apparatus. The laser receiver mast is positioned to intercept a datum laser plane above the tract of land. The datum laser plane is generated by two rotating laser transmitters above the tract of land. The planar position of the laser receiver mast, and thus the earthmoving apparatus, is determined by conventional triangulation techniques.
The vertical intercept point of the laser beam on the laser receiver mast, which is indicative of elevation of the grading implement, is provided to the computer which calculates elevation error of the grading implement based on the cut-fill map and the detected planar position of the apparatus. The elevation error may be communicated to the operator of the earthmoving apparatus who can then make the appropriate adjustments manually or the computer may automatically adjust the elevation of the grading implement to reduce the elevation error.
The just described Davidson system may experience problems when the earthmoving apparatus is filling an area of the tract of land. During filling, the operator of the earthmoving apparatus positions the grading implement at the appropriate level and pushes soil into the area to be filled. However, a problem arises when there is insufficient soil to cover the area to be filled. Since the grading implement remains at the required level, the positioning system of Davidson et al will indicate that the proper contour has been graded when, in fact, the area is below the desired level.
U.S. Pat. No. 5,144,317 issued to Duddek et al discloses a method for determining mining progress in open cast mining using satellite geodesy. The position of an extraction device, such as a bucket wheel of a bucket wheel digger, is monitored by analyzing signals received from at least four satellites. The geometry of the mine during the mining operation may be continuously deduced and displayed on a picture screen. However, the Duddek et al invention calculates the amount of soil, or deposit material, removed during a single cut based on the position and physical dimensions of the bucket wheel. Consequently, as previously discussed with respect to the Davidson et al system, the Duddek et al method fails to address the aforementioned problem of erroneous measurements when there is insufficient soil to cover the area to be filled.
Accordingly, the need exists in the art for an improved earthmoving apparatus and method for grading a tract of land wherein a contour map having cut and fill lines thereon is continually and accurately modified as the earthmoving apparatus traverses the tract of land.